/**
 *  67. 二进制求和
 *  https://leetcode.cn/problems/add-binary/description/
 */
class Solution {
    public String addBinary(String a, String b) {
        StringBuffer ret = new StringBuffer();
        int cur1 = a.length() - 1, cur2 = b.length() - 1, t = 0;
        while(cur1 >= 0 || cur2 >= 0 || t != 0) {
            if(cur1 >= 0) t += a.charAt(cur1--) - '0';
            if(cur2 >= 0) t += b.charAt(cur2--) - '0';

            ret.append((char)(t % 2 + '0'));
            t /= 2;
        }
        return ret.reverse().toString();
    }
}